diff --git a/packages/core/agent-loop/src/agent.ts b/packages/core/agent-loop/src/agent.ts
index 13fd420065..0487f52095 100644
--- a/packages/core/agent-loop/src/agent.ts
+++ b/packages/core/agent-loop/src/agent.ts
@@ -11,7 +11,6 @@ import type {
   AgentStatus,
   CancelOptions,
   InboxTarget,
-  PreStepDecision,
   RequestErrorAction,
 } from '@deepseek-ai/dsh-agent'
 import { Inbox, agentCarrier, agentEvents, assembleContextFor, emitAgentEvent } from '@deepseek-ai/dsh-agent'
@@ -26,10 +25,12 @@ import {
 } from '@deepseek-ai/dsh-llm'
 import type { Scope } from '@deepseek-ai/dsh-scope'
 import { createScope } from '@deepseek-ai/dsh-scope'
-import type { EpochHeader, Session, SessionId, TurnEndReason, UserMessage } from '@deepseek-ai/dsh-session'
+import type { EpochHeader, RequestContext, Session, SessionId, TurnEndReason, UserMessage } from '@deepseek-ai/dsh-session'
 import { canonicalHeader, headerEquals } from '@deepseek-ai/dsh-session'
-import { renderPrompt } from '@deepseek-ai/dsh-system-prompt'
+import { renderContextSnapshot, renderPrompt } from '@deepseek-ai/dsh-system-prompt'
+import type { PromptAssembly } from '@deepseek-ai/dsh-system-prompt'
 import type { Context } from 'cordis'
+import { RuntimeContextProjection } from './runtime-context.ts'
 import { executeToolCalls } from './tool-calls.ts'
 
 type Phase =
@@ -39,6 +40,10 @@ type Phase =
 
 type StepEndReason = Extract<TurnEndReason, { kind: 'completed' | 'max-tokens' }>
 
+type PreparedStep =
+  | { kind: 'reject' }
+  | { kind: 'enter'; messages: UserMessage[]; assembly: PromptAssembly }
+
 /** Remove adapter-derived values before plugins propose the next request config. */
 function requestProposal(header: EpochHeader): LlmCallConfig {
   if (header.adapterDefaults === undefined) return header.config
@@ -60,6 +65,7 @@ export class ReactLoopAgent implements Agent {
 
   /** Whether this loop instance has appended its initial/resume request anchor. */
   private requestHeaderLogged = false
+  private readonly runtimeContext: RuntimeContextProjection
 
   constructor(
     private loopCtx: Context,
@@ -75,6 +81,7 @@ export class ReactLoopAgent implements Agent {
     this.phase = { kind: 'idle', lastTurn }
     this.scope = createScope(loopCtx, this)
     this.ctx = this.scope.ctx.extend({ agent: this })
+    this.runtimeContext = new RuntimeContextProjection(this.ctx, session)
   }
 
   get status(): AgentStatus {
@@ -154,19 +161,25 @@ export class ReactLoopAgent implements Agent {
     }
   }
 
-  private async preStep(target: InboxTarget, position: { turn: number; step: number }): Promise<PreStepDecision> {
+  private async preStep(target: InboxTarget, position: { turn: number; step: number }): Promise<PreparedStep> {
     if (this.phase.kind !== 'running') throw new Error(`agent "${this.id}": pre-step outside running phase`)
     const signal = this.phase.abort.signal
     const claimed = this.inbox.claim(target)
     for (const message of claimed) {
       emitAgentEvent(this.loopCtx, this, 'agent/inbox/claimed', { message, turn: position.turn })
     }
+    const assembly = await this.loopCtx.systemPrompt.assemble(assembleContextFor(this, signal))
+    signal.throwIfAborted()
+    const context = this.runtimeContext.project(renderContextSnapshot(assembly))
     const decision = await agentEvents(this.loopCtx, this).waterfall(
       'agent/pre-step', claimed, { ...position, signal },
-      () => Promise.resolve({ kind: 'enter', messages: claimed }),
+      () => Promise.resolve({
+        kind: 'enter',
+        messages: context === undefined ? claimed : [...claimed, context],
+      }),
     )
     signal.throwIfAborted()
-    return decision
+    return decision.kind === 'reject' ? decision : { ...decision, assembly }
   }
 
   /** Claimed input stays unowned until `turn/start` commits. */
@@ -180,7 +193,7 @@ export class ReactLoopAgent implements Agent {
     const phase = { kind: 'running' as const, abort, turn: lastTurn, step: 0 }
     this.setPhase(phase)
     signal.throwIfAborted()
-    let decision: PreStepDecision
+    let decision: PreparedStep
     try {
       decision = await this.preStep('next-turn', { turn: phase.turn + 1, step: 1 })
       if (decision.kind === 'reject') return false
@@ -205,7 +218,7 @@ export class ReactLoopAgent implements Agent {
           for (const message of decision.messages) {
             this.session.append('user/message', message, { surfaceOp: 'append' })
           }
-          turnEnds = await this.step()
+          turnEnds = await this.step(decision.assembly)
         } finally {
           this.session.append('step/end', { turn, step })
         }
@@ -244,17 +257,16 @@ export class ReactLoopAgent implements Agent {
     return this.inbox.hasPending
   }
 
-  private async step(): Promise<StepEndReason | null> {
+  private async step(assembly: PromptAssembly): Promise<StepEndReason | null> {
     if (this.phase.kind !== 'running') throw new Error(`agent "${this.id}": step outside running phase`)
     const { turn, step, abort: { signal } } = this.phase
     signal.throwIfAborted()
-    const assembly = await this.loopCtx.systemPrompt.assemble(assembleContextFor(this, signal))
-    signal.throwIfAborted()
     const system = renderPrompt(assembly)
+    const boundaryMessages = this.session.deriveMessages()
 
     while (true) {
       const { request, preparedCall } = await this.buildRequest(
-        turn, step, assembly.tools, system, this.session.deriveMessages(), signal,
+        turn, step, assembly.tools, system, boundaryMessages, signal,
       )
       const assembler = new BlockAssembler()
       const chunkSeqs: number[] = []
@@ -383,6 +395,19 @@ export class ReactLoopAgent implements Agent {
     } else if (baseline === undefined || !headerEquals(baseline, header)) {
       this.session.append('request/header', { header, reason: 'change' })
     }
+
+    const contextWindow = preparedCall?.context?.contextWindow
+    const requestContext: RequestContext = {
+      provider: config.provider,
+      model: config.model,
+      ...contextWindow === undefined ? {} : { contextWindow },
+    }
+    const previousContext = session.requestContext()
+    if (previousContext?.provider !== requestContext.provider
+      || previousContext.model !== requestContext.model
+      || previousContext.contextWindow !== requestContext.contextWindow) {
+      session.append('request/context', requestContext)
+    }
     signal.throwIfAborted()
 
     const request = markAgentLoopRequest(deepFreeze({
diff --git a/packages/core/agent-loop/src/runtime-context.ts b/packages/core/agent-loop/src/runtime-context.ts
new file mode 100644
index 0000000000..26c33a18c5
--- /dev/null
+++ b/packages/core/agent-loop/src/runtime-context.ts
@@ -0,0 +1,71 @@
+/**
+ * Durable projection state for dynamic runtime context.
+ * @module @deepseek-ai/dsh-agent-loop/runtime-context
+ */
+
+import { createUserMessage } from '@deepseek-ai/dsh-llm'
+import type { Session, UserMessage } from '@deepseek-ai/dsh-session'
+import { isReplacementSurfaceEvent } from '@deepseek-ai/dsh-session'
+import type { Context } from 'cordis'
+
+const SOURCE = '@deepseek-ai/dsh-system-prompt'
+const CLEARED = 'Current runtime context: none. Earlier runtime-context snapshots no longer apply.'
+
+function isOwned(message: UserMessage): boolean {
+  return message.source.kind === 'plugin' && message.source.plugin === SOURCE
+}
+
+function textOf(message: UserMessage): string | undefined {
+  const [block] = message.content
+  return message.content.length === 1 && block?.type === 'text' ? block.text : undefined
+}
+
+/** Tracks the last retained runtime-context snapshot without owning its commit. */
+export class RuntimeContextProjection {
+  /** `undefined` means no snapshot ever existed; `null` means none is retained. */
+  private retained: { seq: number; text: string | undefined } | null | undefined
+
+  /**
+   * Restore projection state once, then follow authoritative session events.
+   * @param ctx - agent-scoped event context.
+   * @param session - session receiving projected messages.
+   */
+  constructor(ctx: Context, session: Session) {
+    const surface = new Set(session.surface.nodes)
+    for (let index = session.events.length - 1; index >= 0; index -= 1) {
+      const event = session.events[index]
+      if (event?.type !== 'user/message' || !isOwned(event.data)) continue
+      this.retained ??= null
+      if (surface.has(event.seq)) {
+        this.retained = { seq: event.seq, text: textOf(event.data) }
+        break
+      }
+    }
+
+    ctx.on('session/event', (subject, event) => {
+      if (subject !== session) return
+      if (event.type === 'user/message' && isOwned(event.data)) {
+        this.retained = { seq: event.seq, text: textOf(event.data) }
+      } else if (this.retained
+        && isReplacementSurfaceEvent(event)
+        && event.sourceEventSeqs?.includes(this.retained.seq) === true) {
+        this.retained = null
+      }
+    })
+  }
+
+  /**
+   * Create an uncommitted snapshot only when the retained value differs.
+   * @param current - fully rendered dynamic context.
+   * @returns a candidate user message, or `undefined` when no update is needed.
+   */
+  project(current: string): UserMessage | undefined {
+    if (this.retained === undefined && current.length === 0) return
+    const snapshot = current.length === 0 ? CLEARED : current
+    if (this.retained?.text === snapshot) return
+    return createUserMessage({
+      content: [{ type: 'text', text: snapshot }],
+      source: { kind: 'plugin', plugin: SOURCE },
+    })
+  }
+}
diff --git a/packages/core/agent-loop/tests/cancel.spec.ts b/packages/core/agent-loop/tests/cancel.spec.ts
index da5d638d13..69f265ac5a 100644
--- a/packages/core/agent-loop/tests/cancel.spec.ts
+++ b/packages/core/agent-loop/tests/cancel.spec.ts
@@ -1,8 +1,8 @@
 import { createUserMessage } from '@deepseek-ai/dsh-llm'
 /**
  * Tests for the queue-aware `Agent.cancel()` primitive. The default clears
- * queued and steering work, while `keepInbox` preserves pending input and
- * resumes waking turns after the active turn reaches quiescence. The suite
+ * queued and steering work, while `keepInbox` preserves pending input for a
+ * later wake after the active turn reaches quiescence. The suite
  * covers every landing window plus signal reset and `whenIdle()` quiescence.
  * @module dsh-agent-loop/tests/cancel
  */
@@ -284,41 +284,6 @@ describe('Agent.cancel()', () => {
     expect(adapter.requests).toHaveLength(1)
   })
 
-  it('cancel({ keepInbox: true }) aborts the active turn and drains the queued tail in FIFO order', async () => {
-    const adapter = new MockAdapter([
-      'hang',
-      textResponse('second reply'),
-      textResponse('third reply'),
-    ])
-    const ctx = await harness(adapter)
-    const agent = ctx.agentLoop.create(SessionId('keep-inbox-running'), { provider: 'mock', model: 'mock' })
-    const reasons: TurnEndReason[] = []
-    const discards: unknown[] = []
-    ctx.on('session/event', (session, event) => {
-      if (session === agent.session && event.type === 'turn/end') reasons.push(event.data.reason)
-    })
-    ctx.on('agent/inbox/discard', (subject, items) => {
-      if (subject === agent) discards.push(items)
-    })
-
-    send(agent, 'active')
-    await new Promise(resolve => setTimeout(resolve, 30))
-    send(agent, 'queued second')
-    send(agent, 'queued third')
-    const idle = agent.whenIdle()
-    agent.cancel({ kind: 'user' }, { keepInbox: true })
-    await idle
-
-    expect(discards).toEqual([])
-    expect(userTexts(agent)).toEqual(['active', 'queued second', 'queued third'])
-    expect(reasons).toEqual([
-      { kind: 'aborted' },
-      { kind: 'completed' },
-      { kind: 'completed' },
-    ])
-    expect(adapter.requests).toHaveLength(3)
-  })
-
   it('cancel from an assistant/message observer skips execution but balances replay', async () => {
     const adapter = new MockAdapter([
       toolCallResponse('c1', 'danger', {}),
@@ -770,7 +735,7 @@ describe('Agent.cancel()', () => {
     agent.cancel({ kind: 'user' })
     await idle
     const turnEnd = agent.session.events.findLast(event => event.type === 'turn/end')
-    if (stage === 'pre-step') {
+    if (stage === 'pre-step' || stage === 'system-prompt') {
       expect(turnEnd).toBeUndefined()
     } else {
       expect(turnEnd?.type === 'turn/end' && turnEnd.data.reason).toEqual({ kind: 'aborted', reason: { kind: 'user' } })
diff --git a/packages/core/agent-loop/tests/contract-regressions.spec.ts b/packages/core/agent-loop/tests/contract-regressions.spec.ts
index 28c36a24a8..d4e520d958 100644
--- a/packages/core/agent-loop/tests/contract-regressions.spec.ts
+++ b/packages/core/agent-loop/tests/contract-regressions.spec.ts
@@ -1122,7 +1122,7 @@ describe('tool result call identity', () => {
 })
 
 describe('disposal and cancellation during pre-step assembly', () => {
-  it('disposal during system-prompt assembly closes the started step as disposed', { timeout: 30000 }, async () => {
+  it('disposal during system-prompt assembly prevents the turn from opening', { timeout: 30000 }, async () => {
     // Start disposal, then release assembly. Do not await disposal first: it
     // waits for the blocked driver to exit.
     const adapter = new MockAdapter(['hang'])
@@ -1154,7 +1154,7 @@ describe('disposal and cancellation during pre-step assembly', () => {
     ctx.on('session/event', (_s, event) => { if (event.type === 'turn/end') reasons.push(event.data.reason) })
 
     send(agent, 'go')
-    // Give the loop time to enter the step and reach assemble().
+    // Give the loop time to reach pre-step assembly.
     await new Promise(r => setTimeout(r, 50))
 
     // Release assembly before awaiting disposal because disposal joins the blocked driver.
@@ -1165,18 +1165,15 @@ describe('disposal and cancellation during pre-step assembly', () => {
     await driverDone(agent)
     unlisten()
 
-    // Turn boundaries are durable rows; there is no `agent/*` mirror to assert.
     const e = [...agent.session.events]
-    expect(e.filter(x => x.type === 'turn/start')).toHaveLength(1)
-    expect(e.filter(x => x.type === 'turn/end')).toHaveLength(1)
-    const turnEnd = e.findLast(x => x.type === 'turn/end')
-    expect(turnEnd?.type === 'turn/end' && turnEnd.data.reason).toEqual({ kind: 'aborted', reason: { kind: 'disposed' } })
-    expect(e.filter(x => x.type === 'step/start')).toHaveLength(1)
-    expect(e.filter(x => x.type === 'step/end')).toHaveLength(1)
+    expect(e.some(x => x.type === 'turn/start')).toBe(false)
+    expect(e.some(x => x.type === 'turn/end')).toBe(false)
+    expect(e.some(x => x.type === 'step/start')).toBe(false)
+    expect(e.some(x => x.type === 'step/end')).toBe(false)
     expect(e.some(x => x.type === 'assistant/chunk')).toBe(false)
   })
 
-  it('cancel during system-prompt assembly closes the started step as aborted', { timeout: 30000 }, async () => {
+  it('cancel during system-prompt assembly prevents the turn from opening', { timeout: 30000 }, async () => {
     const adapter = new MockAdapter([textResponse('should not appear')])
     let releaseAssemble!: () => void
     const blocker = new Promise<void>(r => void (releaseAssemble = r))
@@ -1215,16 +1212,14 @@ describe('disposal and cancellation during pre-step assembly', () => {
     unlisten()
 
     const e = [...agent.session.events]
-    expect(e.filter(x => x.type === 'turn/start')).toHaveLength(1)
-    expect(e.filter(x => x.type === 'turn/end')).toHaveLength(1)
-    const turnEnd = e.findLast(x => x.type === 'turn/end')
-    expect(turnEnd?.type === 'turn/end' && turnEnd.data.reason).toEqual({ kind: 'aborted', reason: { kind: 'user' } })
-    expect(e.filter(x => x.type === 'step/start')).toHaveLength(1)
-    expect(e.filter(x => x.type === 'step/end')).toHaveLength(1)
+    expect(e.some(x => x.type === 'turn/start')).toBe(false)
+    expect(e.some(x => x.type === 'turn/end')).toBe(false)
+    expect(e.some(x => x.type === 'step/start')).toBe(false)
+    expect(e.some(x => x.type === 'step/end')).toBe(false)
     expect(e.some(x => x.type === 'assistant/chunk')).toBe(false)
     expect(e.some(x => x.type === 'assistant/message')).toBe(false)
     expect(adapter.requests).toHaveLength(0)
-    expect(reasons).toEqual([{ kind: 'aborted', reason: { kind: 'user' } }])
+    expect(reasons).toEqual([])
   })
 
   it('disposal during pre-step prevents the turn from opening', { timeout: 15000 }, async () => {
@@ -1356,14 +1351,10 @@ describe('disposal and cancellation during pre-step assembly', () => {
     await driverDone(agent)
 
     const e = [...agent.session.events]
-    expect(e.filter(x => x.type === 'turn/start')).toHaveLength(1)
-    expect(e.filter(x => x.type === 'turn/end')).toHaveLength(1)
-    // The critical assertions: after disposal, the turn has no assistant
-    // artifacts — the turn ended disposed before the model was invoked.
+    expect(e.some(x => x.type === 'turn/start')).toBe(false)
+    expect(e.some(x => x.type === 'turn/end')).toBe(false)
     expect(e.some(x => x.type === 'assistant/chunk')).toBe(false)
     expect(e.some(x => x.type === 'assistant/message')).toBe(false)
     expect(adapter.requests).toHaveLength(0)
-    // The durable turn/end reason is the authoritative turn-boundary record
-    // (turn boundaries have no agent/* mirror).
   })
 })
diff --git a/packages/core/agent-loop/tests/tool-order.spec.ts b/packages/core/agent-loop/tests/tool-order.spec.ts
index e8a13f6a80..6b9ac94d4b 100644
--- a/packages/core/agent-loop/tests/tool-order.spec.ts
+++ b/packages/core/agent-loop/tests/tool-order.spec.ts
@@ -93,8 +93,7 @@ describe('loop-level canonical tool order', () => {
     expect(Object.isFrozen(adapter.requests[0])).toBe(true)
   })
 
-  it('fails the turn — no model request — when toolOrder names an unregistered tool', async () => {
-    // Unknown tool order fails before step or request creation and returns the agent to idle.
+  it('fails before opening a turn when toolOrder names an unregistered tool', async () => {
     const adapter = new MockAdapter([textResponse('never sent')])
     const ctx = await harness(adapter, ['ghost', TOOL_ORDER_REST])
     registerNamed(ctx, 'alpha')
@@ -103,12 +102,9 @@ describe('loop-level canonical tool order', () => {
     await waitForIdle(ctx, agent)
     expect(adapter.requests).toHaveLength(0)
     expect(foldRequestHeader(agent.session.events)).toBeUndefined()
-    const end = agent.session.events.find(e => e.type === 'turn/end')
-    expect(end?.type === 'turn/end' && end.data.reason).toEqual({
-      kind: 'error',
-      error: 'toolOrder lists unregistered tool "ghost"; known tools: alpha',
-    })
-    expect(agent.session.events.filter(e => e.type === 'step/start')).toHaveLength(1)
-    expect(agent.session.events.filter(e => e.type === 'step/end')).toHaveLength(1)
+    expect(agent.session.events.some(e => e.type === 'turn/start')).toBe(false)
+    expect(agent.session.events.some(e => e.type === 'turn/end')).toBe(false)
+    expect(agent.session.events.some(e => e.type === 'step/start')).toBe(false)
+    expect(agent.session.events.some(e => e.type === 'step/end')).toBe(false)
   })
 })
diff --git a/packages/core/agent-loop/tests/turn-admission.spec.ts b/packages/core/agent-loop/tests/turn-admission.spec.ts
deleted file mode 100644
index e5d4d2ebb3..0000000000
--- a/packages/core/agent-loop/tests/turn-admission.spec.ts
+++ /dev/null
@@ -1,286 +0,0 @@
-import { describe, expect, it } from 'vitest'
-import { Context } from 'cordis'
-import AgentRegistry, { type Agent, type InboxItem } from '@deepseek-ai/dsh-agent'
-import AgentLoop from '@deepseek-ai/dsh-agent-loop'
-import LlmService, { createUserMessage } from '@deepseek-ai/dsh-llm'
-import SessionStore, { SessionId } from '@deepseek-ai/dsh-session'
-import SystemPrompt from '@deepseek-ai/dsh-system-prompt'
-import ToolRegistry from '@deepseek-ai/dsh-tools'
-import { MockAdapter, textResponse } from './mock-adapter.ts'
-
-async function harness(adapter: MockAdapter): Promise<Context> {
-  const ctx = new Context()
-  await ctx.plugin(LlmService)
-  await ctx.plugin(SessionStore)
-  await ctx.plugin(SystemPrompt)
-  await ctx.plugin(ToolRegistry)
-  await ctx.plugin(AgentRegistry)
-  await ctx.plugin(AgentLoop, { agents: [] })
-  ctx.llm.registerAdapter(['mock'], adapter)
-  return ctx
-}
-
-function prompt(agent: Agent, text: string): void {
-  agent.followup(createUserMessage({
-    content: [{ type: 'text', text }],
-    source: { kind: 'user' },
-  }))
-}
-
-function itemText(item: InboxItem): string {
-  return item.message.content.flatMap(block => block.type === 'text' ? [block.text] : []).join('')
-}
-
-interface InboxRecording {
-  readonly events: string[]
-  readonly enqueued: InboxItem['id'][]
-  readonly dequeued: InboxItem['id'][]
-  readonly discarded: InboxItem['id'][]
-}
-
-/** Record the complete inbox lifecycle of one agent for order and identity assertions. */
-function recordInbox(ctx: Context): InboxRecording {
-  const events: string[] = []
-  const enqueued: InboxItem['id'][] = []
-  const dequeued: InboxItem['id'][] = []
-  const discarded: InboxItem['id'][] = []
-  ctx.on('agent/inbox/enqueue', (_agent, item) => {
-    events.push(`enqueue:${item.placement}:${itemText(item)}`)
-    enqueued.push(item.id)
-  })
-  ctx.on('agent/inbox/dequeue', (_agent, item) => {
-    events.push(`dequeue:${itemText(item)}`)
-    dequeued.push(item.id)
-  })
-  ctx.on('agent/inbox/discard', (_agent, items) => {
-    events.push(`discard:${items.map(itemText).join(',')}`)
-    discarded.push(...items.map(item => item.id))
-  })
-  return { events, enqueued, dequeued, discarded }
-}
-
-/** Text of every ordinary prompt the log admitted, in durable order. */
-function promptTexts(agent: Agent): string[] {
-  return agent.session.events.flatMap(event => event.type === 'user/message'
-    ? event.data.content.flatMap(block => block.type === 'text' ? [block.text] : [])
-    : [])
-}
-
-describe('idle turn admission reservation', () => {
-  it('holds later waking prompts in the FIFO until release', async () => {
-    const adapter = new MockAdapter([textResponse('first'), textResponse('second')])
-    const ctx = await harness(adapter)
-    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })
-    const inbox = recordInbox(ctx)
-
-    const release = agent.reserveTurnAdmission()
-    expect(release).toBeDefined()
-
-    prompt(agent, 'first prompt')
-    prompt(agent, 'second prompt')
-    expect(agent.acceptsNextStep).toBe(false)
-    await new Promise<void>((resolve) => { setTimeout(resolve, 5) })
-
-    expect(agent.status).toBe('idle')
-    expect(adapter.requests).toHaveLength(0)
-    expect(agent.session.events).toHaveLength(0)
-    expect(inbox.events).toEqual([
-      'enqueue:queued:first prompt',
-      'enqueue:queued:second prompt',
-    ])
-
-    release?.()
-    await agent.whenIdle()
-
-    expect(promptTexts(agent)).toEqual(['first prompt', 'second prompt'])
-    expect(agent.session.events.flatMap(event =>
-      event.type === 'turn/start' ? [event.data.turn] : [])).toEqual([1, 2])
-    expect(inbox.events).toEqual([
-      'enqueue:queued:first prompt',
-      'enqueue:queued:second prompt',
-      'dequeue:first prompt',
-      'dequeue:second prompt',
-    ])
-    expect(inbox.dequeued).toEqual(inbox.enqueued)
-    expect(inbox.discarded).toEqual([])
-  })
-
-  it('refuses acquisition when an accepted waking prompt still owns the next turn', async () => {
-    const adapter = new MockAdapter([textResponse('ok')])
-    const ctx = await harness(adapter)
-    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })
-
-    prompt(agent, 'accepted first')
-    expect(agent.status).toBe('idle')
-    expect(agent.reserveTurnAdmission()).toBeUndefined()
-
-    await agent.whenIdle()
-    expect(adapter.requests).toHaveLength(1)
-  })
-
-  it('refuses acquisition while a turn is running', async () => {
-    const adapter = new MockAdapter([textResponse('ok')])
-    const ctx = await harness(adapter)
-    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })
-    const reserved: unknown[] = []
-    ctx.on('agent/step', () => {
-      reserved.push(agent.reserveTurnAdmission())
-    })
-
-    prompt(agent, 'running')
-    await agent.whenIdle()
-
-    expect(agent.status).toBe('idle')
-    expect(reserved).toEqual([undefined])
-  })
-
-  it('refuses a second reservation and releases idempotently', async () => {
-    const adapter = new MockAdapter([textResponse('ok')])
-    const ctx = await harness(adapter)
-    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })
-
-    const release = agent.reserveTurnAdmission()
-    expect(agent.reserveTurnAdmission()).toBeUndefined()
-    prompt(agent, 'queued behind the reservation')
-
-    release?.()
-    release?.()
-    await agent.whenIdle()
-
-    expect(promptTexts(agent)).toEqual(['queued behind the reservation'])
-    expect(adapter.requests).toHaveLength(1)
-    const second = agent.reserveTurnAdmission()
-    expect(second).toBeDefined()
-    second?.()
-  })
-
-  it('ignores a stale release once a later reservation owns the boundary', async () => {
-    const adapter = new MockAdapter([textResponse('ok')])
-    const ctx = await harness(adapter)
-    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })
-
-    const stale = agent.reserveTurnAdmission()
-    stale?.()
-    const live = agent.reserveTurnAdmission()
-    prompt(agent, 'held by the live reservation')
-    stale?.()
-    await new Promise<void>((resolve) => { setTimeout(resolve, 5) })
-
-    expect(adapter.requests).toHaveLength(0)
-    live?.()
-    await agent.whenIdle()
-    expect(adapter.requests).toHaveLength(1)
-  })
-
-  it('acquires beside quiet queued work and leaves it queued', async () => {
-    const adapter = new MockAdapter([textResponse('ok')])
-    const ctx = await harness(adapter)
-    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })
-
-    agent.send(createUserMessage({
-      content: [{ type: 'text', text: 'quiet' }],
-      source: { kind: 'user' },
-    }), {
-      target: 'next-turn',
-      wakeup: false,
-    })
-    const release = agent.reserveTurnAdmission()
-    expect(release).toBeDefined()
-
-    release?.()
-    await agent.whenIdle()
-    expect(adapter.requests).toHaveLength(0)
-  })
-
-  it('makes whenIdle() wait for release without spinning on a settled promise', async () => {
-    const adapter = new MockAdapter([textResponse('ok')])
-    const ctx = await harness(adapter)
-    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })
-    const machine = agent as Agent & { done: Promise<void> }
-    let backing = machine.done
-    let reads = 0
-    Object.defineProperty(agent, 'done', {
-      configurable: true,
-      get(): Promise<void> {
-        reads += 1
-        return backing
-      },
-      set(value: Promise<void>) {
-        backing = value
-      },
-    })
-
-    const release = agent.reserveTurnAdmission()
-    prompt(agent, 'waiting for the reservation')
-    let settled = false
-    const idle = agent.whenIdle().then(() => { settled = true })
-    for (let tick = 0; tick < 5; tick += 1) {
-      await new Promise<void>((resolve) => { setTimeout(resolve, 1) })
-    }
-
-    expect(settled).toBe(false)
-    expect(reads).toBeLessThanOrEqual(2)
-
-    release?.()
-    await idle
-    expect(settled).toBe(true)
-    expect(adapter.requests).toHaveLength(1)
-  })
-
-  it('resolves whenIdle() after release with nothing queued', async () => {
-    const adapter = new MockAdapter([])
-    const ctx = await harness(adapter)
-    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })
-
-    const release = agent.reserveTurnAdmission()
-    let settled = false
-    const idle = agent.whenIdle().then(() => { settled = true })
-    await new Promise<void>((resolve) => { setTimeout(resolve, 5) })
-    expect(settled).toBe(false)
-
-    release?.()
-    await idle
-    expect(agent.status).toBe('idle')
-  })
-
-  it('lets cancellation discard held prompts and keeps the boundary quiet', async () => {
-    const adapter = new MockAdapter([])
-    const ctx = await harness(adapter)
-    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })
-    const inbox = recordInbox(ctx)
-
-    const release = agent.reserveTurnAdmission()
-    prompt(agent, 'discarded while held')
-    agent.cancel({ kind: 'user' })
-
-    expect(inbox.events).toEqual([
-      'enqueue:queued:discarded while held',
-      'discard:discarded while held',
-    ])
-    expect(inbox.discarded).toEqual(inbox.enqueued)
-    expect(inbox.dequeued).toEqual([])
-
-    release?.()
-    await agent.whenIdle()
-    expect(adapter.requests).toHaveLength(0)
-    expect(agent.session.events).toHaveLength(0)
-  })
-
-  it('disposes the agent without waiting for the reservation to be released', async () => {
-    const adapter = new MockAdapter([])
-    const ctx = await harness(adapter)
-    const handle = await ctx.agents.create({
-      sessionId: SessionId('a1'),
-      agentOptions: { provider: 'mock', model: 'mock' },
-    })
-    const { agent } = handle
-
-    const release = agent.reserveTurnAdmission()
-    prompt(agent, 'discarded by disposal')
-    await handle.dispose()
-
-    expect(ctx.agents.list()).toEqual([])
-    expect(adapter.requests).toHaveLength(0)
-    release?.()
-  })
-})
diff --git a/packages/core/session/src/index.ts b/packages/core/session/src/index.ts
index d1bafae56a..13fe7a30a3 100644
--- a/packages/core/session/src/index.ts
+++ b/packages/core/session/src/index.ts
@@ -13,7 +13,7 @@ import { scopeOf, scopeTarget } from '@deepseek-ai/dsh-scope'
 import type { Scoped } from '@deepseek-ai/dsh-scope'
 import type { Message } from '@deepseek-ai/dsh-llm'
 import { SESSION_FORMAT_VERSION, SessionId } from './types.ts'
-import type { CreateSessionOptions, EpochHeader, SessionEvent, SessionEventMap, SessionEventType, SessionHeader, SurfaceIntent, SurfaceEventType } from './types.ts'
+import type { CreateSessionOptions, EpochHeader, RequestContext, SessionEvent, SessionEventMap, SessionEventType, SessionHeader, SurfaceIntent, SurfaceEventType } from './types.ts'
 import { snapshotJsonValue } from './json.ts'
 import { SurfaceManager } from './surface.ts'
 import type { SessionSurface } from './surface.ts'
@@ -392,7 +392,7 @@ export class Session {
   readonly firstLiveSeq: number
 
   constructor(id: SessionId, seed?: readonly SessionEvent[], header?: SessionHeader) {
-    if (seed) {
+    if (seed !== undefined) {
       // Validate the seed to the SAME invariants `append` enforces, so a
       // replay/fork (`ctx.sessions.create(id, { seed })`) cannot construct a
       // live log that no persistence backend could store: each event's `data`
@@ -429,7 +429,7 @@ export class Session {
     // captures the creation seed: no load-time write. Re-marking is skipped
     // because a cold session is resumed on first touch, so repeatedly opening
     // one must not grow its log per open.
-    if (this.firstLiveSeq > 0 && this.log.at(-1)?.type !== 'session/end-seed') {
+    if (seed !== undefined && this.log.at(-1)?.type !== 'session/end-seed') {
       this.append('session/end-seed', {})
     }
   }
@@ -566,6 +566,25 @@ export class Session {
     return this.headerFold
   }
 
+  /** Cached fold of `request/context` events. */
+  private contextFold: RequestContext | undefined
+  private contextFoldSeq = 0
+
+  /**
+   * Return the latest resolved route metadata, or `undefined` before the first
+   * `request/context` event. Each event is folded once.
+   * @returns the latest immutable route metadata.
+   */
+  requestContext(): RequestContext | undefined {
+    if (this.contextFoldSeq < this.log.length) {
+      for (const event of this.log.slice(this.contextFoldSeq)) {
+        if (event.type === 'request/context') this.contextFold = deepFreeze({ ...event.data })
+      }
+      this.contextFoldSeq = this.log.length
+    }
+    return this.contextFold
+  }
+
   /** The derived-message cache: frozen projections, extended per unseen node. */
   private derived: Message[] = []
   /** Surface position (nodes projected) the cache has reached. */
diff --git a/packages/core/session/src/invariant.ts b/packages/core/session/src/invariant.ts
index c454ad6533..f7e7292bc4 100644
--- a/packages/core/session/src/invariant.ts
+++ b/packages/core/session/src/invariant.ts
@@ -149,7 +149,8 @@ function validateEvent(
       break
     case 'steering/message':
     case 'todo/write':
-    case 'request/header': {
+    case 'request/header':
+    case 'request/context': {
       if (trace.openTurn === null) {
         fail(`${event.type} appended outside any open turn (core execution events must be turn-enclosed)`)
       }
diff --git a/packages/core/session/src/types.ts b/packages/core/session/src/types.ts
index d814e612f1..691861e8b4 100644
--- a/packages/core/session/src/types.ts
+++ b/packages/core/session/src/types.ts
@@ -151,6 +151,16 @@ export interface EpochHeader {
   tools?: ToolSchema[]
 }
 
+/** Registration-bound metadata for one resolved model route. */
+export interface RequestContext {
+  /** Registered provider route the metadata belongs to. */
+  provider: string
+  /** Provider-owned model id the metadata belongs to. */
+  model: string
+  /** Maximum combined request and response context in tokens, when advertised. */
+  contextWindow?: number
+}
+
 /**
  * Why a `request/header` snapshot was appended: `'initial'` — the log's first
  * header (a new conversation); `'resume'` — a loop instance's first request
@@ -233,6 +243,11 @@ export interface SessionEventMap {
    * It is log-only; the latest snapshot reconstructs the request header.
    */
   'request/header': { header: EpochHeader; reason: RequestHeaderReason }
+  /**
+   * Route metadata for the next request, logged only when the route or capacity
+   * changes. It does not participate in request reconstruction or header equality.
+   */
+  'request/context': RequestContext
   /**
    * Marks the end of a constructor seed. Events before it have smaller seq
    * values and came from the seed (resume, fork, or replay); this lifecycle
diff --git a/packages/core/system-prompt/src/index.ts b/packages/core/system-prompt/src/index.ts
index 2e4e5e65b7..cb191bcada 100644
--- a/packages/core/system-prompt/src/index.ts
+++ b/packages/core/system-prompt/src/index.ts
@@ -1,5 +1,5 @@
 /**
- * Registry for ordered prompt sections, tool schemas, and prompt variables.
+ * Registry for ordered system sections, dynamic context, tool schemas, and prompt variables.
  *
  * @module @deepseek-ai/dsh-system-prompt
  */
@@ -17,7 +17,7 @@ declare module 'cordis' {
 
   interface Events {
     /**
-     * Expert waterfall over the assembled sections, tools, and variables.
+     * Expert waterfall over the assembled sections, contexts, tools, and variables.
      * Scope-filtered dispatch (`@deepseek-ai/dsh-scope`): scoped listeners
      * receive only that scope's assemblies. The returned value is authoritative.
      * A supplied signal controls only this explicit assembly request and must not
@@ -65,6 +65,16 @@ export interface PromptSection {
   readonly text: string | ((context: AssembleContext) => string)
 }
 
+/** Dynamic model context materialized as a durable user-role snapshot. */
+export interface PromptContext {
+  /** Unique name — a duplicate registration throws (see {@link SystemPrompt.context}). */
+  readonly name: string
+  /** Contexts are joined in ascending order. */
+  readonly order: number
+  /** Static text or a provider evaluated for each assembly. Empty text contributes nothing. */
+  readonly text: string | ((context: AssembleContext) => string)
+}
+
 /** One section of an assembly: {@link PromptSection} with its text resolved. */
 export interface AssembledSection {
   /** The contributing section's unique name. */
@@ -73,6 +83,14 @@ export interface AssembledSection {
   text: string
 }
 
+/** One resolved dynamic context contribution. */
+export interface AssembledContext {
+  /** The contributing context's unique name. */
+  name: string
+  /** The resolved text before variable interpolation. */
+  text: string
+}
+
 /** Tool schemas visible in one assembly and their pre-restriction name set. */
 export interface ToolProviderResult {
   /** The schemas this provider contributes to THIS assembly. */
@@ -82,11 +100,12 @@ export interface ToolProviderResult {
 }
 
 /**
- * Merge-extensible assembled prompt. Sections remain uninterpolated until
- * {@link renderPrompt}; tools are already in canonical model-facing order.
+ * Merge-extensible assembled model input. Sections and contexts remain
+ * uninterpolated until rendered; tools are already in canonical order.
  */
 export interface PromptAssembly {
   sections: AssembledSection[]
+  contexts: AssembledContext[]
   tools: ToolSchema[]
   variables: Record<string, string | undefined>
 }
@@ -170,14 +189,32 @@ export interface Config {
  */
 export function renderPrompt(assembly: PromptAssembly): string {
   return assembly.sections
-    .map(section => interpolate(section, assembly.variables))
+    .map(section => interpolate(section, assembly.variables, 'section'))
     .filter(text => text.length > 0)
     .join('\n\n')
 }
 
-/** Interpolate one section's `{{variable}}` references (see {@link renderPrompt}). */
-function interpolate(section: AssembledSection, variables: Record<string, string | undefined>): string {
-  const text = section.text
+/**
+ * Render the complete dynamic context snapshot.
+ * @param assembly - the assembly whose contexts and variables to render.
+ * @returns the current full snapshot, or `''` when no context is active.
+ */
+export function renderContextSnapshot(assembly: PromptAssembly): string {
+  const body = assembly.contexts
+    .map(context => interpolate(context, assembly.variables, 'context'))
+    .filter(text => text.length > 0)
+    .join('\n\n')
+  if (body.length === 0) return ''
+  return `Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\n${body}`
+}
+
+/** Interpolate one section or context and attribute diagnostics to its owner. */
+function interpolate(
+  input: AssembledSection | AssembledContext,
+  variables: Record<string, string | undefined>,
+  kind: 'section' | 'context',
+): string {
+  const text = input.text
   let result = ''
   let last = 0
   for (let open = text.indexOf('{{'); open >= 0; open = text.indexOf('{{', last)) {
@@ -185,7 +222,7 @@ function interpolate(section: AssembledSection, variables: Record<string, string
     if (group === null) {
       // A later closing brace makes this malformed; otherwise it is literal prose.
       if (text.indexOf('}}', open + 2) >= 0) {
-        throw new Error(`malformed prompt variable reference at "${text.slice(open, open + 16)}…" in section "${section.name}" (references are complete simple {{name}} groups)`)
+        throw new Error(`malformed prompt variable reference at "${text.slice(open, open + 16)}…" in ${kind} "${input.name}" (references are complete simple {{name}} groups)`)
       }
       result += text.slice(last, open + 2)
       last = open + 2
@@ -194,16 +231,16 @@ function interpolate(section: AssembledSection, variables: Record<string, string
     // `{{}}` yields an empty name and follows the malformed-reference path.
     const name = group[0].slice(2, -2)
     if (!VARIABLE_NAME.test(name)) {
-      throw new Error(`malformed prompt variable reference "{{${name}}}" in section "${section.name}" (variable names match ${String(VARIABLE_NAME)})`)
+      throw new Error(`malformed prompt variable reference "{{${name}}}" in ${kind} "${input.name}" (variable names match ${String(VARIABLE_NAME)})`)
     }
     // Do not resolve unregistered names through Object.prototype.
     if (!Object.hasOwn(variables, name)) {
       const known = Object.keys(variables)
-      throw new Error(`unknown prompt variable "{{${name}}}" in section "${section.name}"; registered variables: ${known.length > 0 ? known.join(', ') : '(none)'}`)
+      throw new Error(`unknown prompt variable "{{${name}}}" in ${kind} "${input.name}"; registered variables: ${known.length > 0 ? known.join(', ') : '(none)'}`)
     }
     const value = variables[name]
     if (value === undefined) {
-      throw new Error(`prompt variable "{{${name}}}" has no value for this assembly (section "${section.name}")`)
+      throw new Error(`prompt variable "{{${name}}}" has no value for this assembly (${kind} "${input.name}")`)
     }
     result += text.slice(last, open) + value
     last = open + group[0].length
@@ -220,6 +257,7 @@ type VariableProvider = (context: AssembleContext) => string | undefined
 /** All prompt registrations owned by one global or scoped layer. */
 class PromptLayer implements ScopeLayer {
   readonly sections: NamedEntries<PromptSection>
+  readonly contexts: NamedEntries<PromptContext>
   readonly toolProviders = new AnonymousEntries<ToolProvider>()
   readonly variables: NamedEntries<VariableProvider>
 
@@ -231,6 +269,9 @@ class PromptLayer implements ScopeLayer {
     this.sections = new NamedEntries(name => new Error(scope === undefined
       ? `prompt section "${name}" is already registered (for a per-agent override, register through that agent's \`agent.ctx\` instead)`
       : `prompt section "${name}" is already registered in this scope`))
+    this.contexts = new NamedEntries(name => new Error(scope === undefined
+      ? `prompt context "${name}" is already registered (for a per-agent override, register through that agent's \`agent.ctx\` instead)`
+      : `prompt context "${name}" is already registered in this scope`))
     this.variables = new NamedEntries(name => new Error(scope === undefined
       ? `prompt variable "${name}" is already registered (for a per-agent value, register through that agent's \`agent.ctx\` instead)`
       : `prompt variable "${name}" is already registered in this scope`))
@@ -239,6 +280,7 @@ class PromptLayer implements ScopeLayer {
   /** @returns whether this layer owns no prompt registrations. */
   isEmpty(): boolean {
     return this.sections.isEmpty()
+      && this.contexts.isEmpty()
       && this.toolProviders.isEmpty()
       && this.variables.isEmpty()
   }
@@ -297,6 +339,23 @@ export class SystemPrompt extends Service {
     )
   }
 
+  /**
+   * Register ordered dynamic context in the calling context's scope. Scoped
+   * entries shadow global entries with the same name.
+   * @param context - the context contribution to register.
+   * @returns the exact Cordis effect disposer.
+   */
+  context(context: PromptContext): () => void {
+    if (!Number.isFinite(context.order)) {
+      throw new TypeError(`prompt context "${context.name}" order must be a finite number`)
+    }
+    return this.layers.effect(
+      this.ctx,
+      layer => layer.contexts.insert(context.name, context),
+      { label: 'systemPrompt.context()' },
+    )
+  }
+
   /**
    * Register a tool-schema provider in the calling context's scope. Global and
    * matching scoped providers both contribute; returning the reserved
@@ -352,6 +411,7 @@ export class SystemPrompt extends Service {
     }
     // Scoped sections shadow globals before the stable order sort.
     const sectionByName = this.layers.merge(scope, layer => layer.sections)
+    const contextByName = this.layers.merge(scope, layer => layer.contexts)
     // Validate order against pre-restriction names while collecting visible schemas.
     const providers = [
       ...this.layers.global.toolProviders.values(),
@@ -377,6 +437,12 @@ export class SystemPrompt extends Service {
           name: section.name,
           text: typeof section.text === 'function' ? section.text(context) : section.text,
         })),
+      contexts: [...contextByName.values()]
+        .sort((a, b) => a.order - b.order)
+        .map(entry => ({
+          name: entry.name,
+          text: typeof entry.text === 'function' ? entry.text(context) : entry.text,
+        })),
       tools: orderTools(collected, this.toolOrder, knownNames),
       variables,
     }
diff --git a/packages/core/system-prompt/src/invariant.ts b/packages/core/system-prompt/src/invariant.ts
index e199cc98b4..04dc65e7ad 100644
--- a/packages/core/system-prompt/src/invariant.ts
+++ b/packages/core/system-prompt/src/invariant.ts
@@ -22,6 +22,14 @@ function validateAssembly(assembly: PromptAssembly, fail: InvariantFailure): voi
     if (typeof section.text !== 'string') fail(`assembled section ${JSON.stringify(section.name)} text must be a string`)
   }
 
+  const contextNames = new Set<string>()
+  for (const context of assembly.contexts) {
+    if (context.name.length === 0) fail('assembled context names must be non-empty')
+    if (contextNames.has(context.name)) fail(`assembled context name ${JSON.stringify(context.name)} is duplicated`)
+    contextNames.add(context.name)
+    if (typeof context.text !== 'string') fail(`assembled context ${JSON.stringify(context.name)} text must be a string`)
+  }
+
   for (const tool of assembly.tools) {
     if (tool.name.length === 0) fail('assembled tool names must be non-empty')
   }